Age Determination of Caribou by Annulations in Dental Cementum

Abstract

The ages of 902 barren-ground caribou (Rangifer tarandus groenlandicus) were determined by examination of histological preparations of dental cementum. The resultant interpretation of the timing of deposition for cemental annulations and the occurrence of the first winter rest line were not in agreement with the only reported study of dental cementum in barren-ground caribou. The findings in this study are, however, the same as for Norwegian reindeer (R. t. spp.). Cementum was deposited on the unerupted first incisor (il) by the 5th month of life, and the first annulus was present by the 10th month. The same timing pertained to cemental deposition and the presence of the first annulus in the first molar (ml). Species-specific problems were encountered and solved for storage, decalcification, dehydration, sectioning, and staining of teeth. The mandibular teeth were decalcified in a 5 percent solution of 67 percent nitric acid and sectioned on a cryostat at about -30 C. The sections were stained with Harris hematoxylin and Eosin Y, mounted with Fisher's Permount, and examined with a microscope at powers ranging from 100X to 400X. The time for both decalcification and staining was very critical and varied considerably among individual teeth. Cemental annuli in sagittal tooth sections were considerably more distinct and easier to read than cross sections. The chronological sequence of the layering of two types of cement allowed the use of the technique with a high degree of confidence. J. WILDL. MANAGE. 38(1):47-53 Ages were assigned to 902 barren-ground caribou from north-central mainland Canada (Miller 1972) by counting seasonal annuli in histological sections of the dental cementum of the mandibular teeth. The age determinations were used to better evaluate population dynamics. Only two studies (McEwan 1963, Reimers and Nordby 1968) have reported on age determinations of Rangifer by examination of dental cementum. McEwan (1963) working on barren-ground caribou in Canada used two techniques. First, he sawed and ground sections of the first incisor using the method described by Fisher and Mackenzie (1954). Secondly, about 100 incisor teeth were decalcified in a solution of 30 percent formic acid for 24 hours and 7-micron sections were cut and stained with Delafield's hematoxylin. In both cases, McEwan found annuli in the dentine and cementum of the tooth sections. More recently, Reimers and Nordby (1968) used a rapid freeze-sectioning technique for detecting annuli in the cementum of the first incisors of Norwegian reindeer. I thank the other members of the Canadian Wildlife Service Caribou Research team: T. C. Dauphine, D. M. Lamperd, A. H. Macpherson, D. R. Miller, G. R. Parker, and G. D. Tessier for their assistance in obtaining the dentary material in the collection. I am especially indebted to D. M. Lamperd and G. D. Tessier for their assistance in the field and laboratory. L. P. E. Choquette, Pathology Section, Canadian Wildlife Service, provided many valuable services throughout the course of the study. E. Broughton and J. P. Couillard, Pathology Section, Canadian Wildlife Service, assisted both in the field and laboratory. Figs. 1-4 were photographed by G. Ben, Department of Biology, University of Ottawa. I thank H. J. Boyd and D. R. Flook, Canadian Wildlife Service, for their help with the manuscript.